In general, it is known to provide heating for the passenger compartment of a motor vehicle by deviating engine coolant through a heater core which then exchanges heat with air entering the passenger compartment. WO-A-95/24323 describes a system for providing initial or supplemental heating using energy supplied by the compressor of the refrigerant fluid of an air conditioning system, and exchanging this energy with air passing through the inside heat exchanger of the air conditioning system. This heating process makes no use of the outside heat exchanger of the air conditioning system, and only uses the compressor, the inside heat exchanger and an expansion device calibrated in such a way that only refrigerant fluid vapour leaves the inside heat exchanger and passes into the compressor.
Another known supplemental heating system uses the energy of an air conditioning loop called a heat pump. In this case, the inside heat exchanger condenses the refrigerant and exchanges the energy with cold air passing through he inside heat exchanger. The outside heat exchanger can get very cold during this operation, and it is possible that the humidity of the air freezes and blocks the core of the outside heat exchanger, preventing any effective heat exchange. Defrosting of the outside heat exchanger can be achieved by reversing the cycle, which leads to a heating of the outside heat exchanger, but also results in cooling of the inside heat exchanger, and hence cooling of the passenger compartment.
For clarification, the inside heat exchanger is the heat exchanger normally located inside the passenger compartment, and the outside heat exchanger is the heat exchanger normally located outside the passenger compartment.